The invention relates to the continuous casting of metals, and particular it relates to a bottomless mold having walls which are subjected to intensive cooling, wherewith the solidification of the liquid metal which is cast in a continuous casting machine is begun in the mold.
Known continuous casting molds for steel slab ingot (a product having rectangular cross section and low ratio of thickness to width) are formed of an assembly of four plates comprised of a metal which is a good heat conductor, e.g. copper or a copper alloy. They are intensely cooled by circulating cooling fluid (usually water). The four plates define a casting space into which, when the liquid metal is introduced, the metal begins to solidify at the surfaces of said plates which face the casting space. The cooling water circulates in vertical channels provided in the interior of the plates, with the water flow proceeding from the bottom to the top of the mold.
A disadvantage of this known configuration is that the water never reaches the level of the uppermost regions of the plates. Consequently, these uppermost regions are insufficiently cooled to tolerate being contacted with the liquid metal being solidified. Therefore care must be taken to ensure that the liquid metal surface (the meniscus) in the mold is low enough so that product solidification can begin under suitable conditions without degradation of the mold itself. This renders useless some of the available height of the mold.
This disadvantage is particularly significant when a mold of the general type described is used in an installation of the type designated "semi-continuous casting". In such facilities, a "feeder" enclosure (feeder bush) comprised of a refractory material is mounted immediately above the part of the mold comprised of metal plates which are cooled by the circulating cooling fluid, to provide an extension of the casting space. This "feeder" serves to provide a reserve of liquid metal above the metal part of the mold. The solidification of the product will occur only in the metal part, but the meniscus is raised to a point in the "feeder" structure. This arrangement provides numerous advantages, among which are:
The solidification will begin at a fixed level, namely the upper limit of the metal plates of the mold, and will no longer depend on fluctuations in the level of the meniscus which are unavoidable in classical apparatus; PA0 The end of the conduit through which the steel is introduced to the mold is maintained in the interior of the "feeder" structure, whereby turbulence which tends to occur in connection with the introduction of the steel is afforded time to subside before the steel reaches the upper part of the plates.
These advantages result in a relatively quiescent flow regime of the liquid metal at the level where the solidification begins, which contributes to good quality of the solidified product, in particular good surface regularity. However, in order to benefit fully from the augmented structure employing a "feeder" bush, the cooling capacity in the upper part of the metal plates of the mold must be optimal in order that the solidification begin there in a definitive and concerted manner. As mentioned above, this regularity is not exhibited with plates of the classical type, because the cooling water does not reach the uppermost region of the mold structure formed by said plates. Accordingly, not only is the desired regularity not achieved but the risk of overheating and rapid degradation of the upper region of the plates is enhanced when a mold of the described classical type is used under a refractory "feeder" bush.